1,050 research outputs found
Temperature dependence of coherent oscillations in Josephson phase qubits
We experimentally investigate the temperature dependence of Rabi oscillations
and Ramsey fringes in superconducting phase qubits driven by microwave pulses.
In a wide range of temperatures, we find that both the decay time and the
amplitude of these coherent oscillations remain nearly unaffected by thermal
fluctuations. The oscillations are observed well above the crossover
temperature from thermally activated escape to quantum tunneling for undriven
qubits. In the two-level limit, coherent qubit response rapidly vanishes as
soon as the energy of thermal fluctuations kT becomes larger than the energy
level spacing of the qubit. Our observations shed new light on the origin of
decoherence in superconducting qubits. The experimental data suggest that,
without degrading already achieved coherence times, phase qubits can be
operated at temperatures much higher than those reported till now.Comment: 4 pages, 4 figure
Measuring the temperature dependence of individual two-level systems by direct coherent control
We demonstrate a new method to directly manipulate the state of individual
two-level systems (TLS) in phase qubits. It allows one to characterize the
coherence properties of TLS using standard microwave pulse sequences, while the
qubit is used only for state readout. We apply this method to measure the
temperature dependence of TLS coherence for the first time. The energy
relaxation time is found to decrease quadratically with temperature for
the two TLS studied in this work, while their dephasing time measured in Ramsey
and spin-echo experiments is found to be limited at all temperatures.Comment: 4 pages, 5 figure
Enhanced Macroscopic Quantum Tunneling in BiSrCaCuO Intrinsic Josephson Junction Stacks
We have investigated macroscopic quantum tunneling in
BiSrCaCuO intrinsic Josephson junctions at millikelvin
temperatures using microwave irradiation. Measurements show that the escape
rate for uniformly switching stacks of N junctions is about times higher
than that of a single junction having the same plasma frequency. We argue that
this gigantic enhancement of macroscopic quantum tunneling rate in stacks is
boosted by current fluctuations which occur in the series array of junctions
loaded by the impedance of the environment.Comment: 4 pages and 5 figure
Entangling microscopic defects via a macroscopic quantum shuttle
In the microscopic world, multipartite entanglement has been achieved with
various types of nanometer sized two-level systems such as trapped ions, atoms
and photons. On the macroscopic scale ranging from micrometers to millimeters,
recent experiments have demonstrated bipartite and tripartite entanglement for
electronic quantum circuits with superconducting Josephson junctions. It
remains challenging to bridge these largely different length scales by
constructing hybrid quantum systems. Doing this may allow for manipulating the
entanglement of individual microscopic objects separated by macroscopically
large distances in a quantum circuit. Here we report on the experimental
demonstration of induced coherent interaction between two intrinsic two-level
states (TLSs) formed by atomic-scale defects in a solid via a superconducting
phase qubit. The tunable superconducting circuit serves as a shuttle
communicating quantum information between the two microscopic TLSs. We present
a detailed comparison between experiment and theory and find excellent
agreement over a wide range of parameters. We then use the theoretical model to
study the creation and movement of entanglement between the three components of
the quantum system.Comment: 11 pages, 5 figure
Evaluation of Cultural Impact on Regional Economic Development in Russia
Paper is devoted to Dependence of economic development of the Russian regions on their cultural level indicators. It determines and analyzes the influence degree of cultural components of the region development on its economic factors. The investigated statistical base consists of selected cultural and economic indices taken in the period of 2000-2015 years. The hypothesis of significant influence degree of the visits to museums and in particular, theatres number, on the amount of implemented innovational technologies was confirmed. A hypothesis about the close relationship between the volumes of expenditures of the Russian budget for culture and the level of research and development work, as well as directly the number of innovative industrial technologies introduced was confirmed. Hypotheses about the close interaction of cultural indices and such macroeconomic parameters as GDP growth, the volume of the capital investments have not been confirmed. A weak correlation between library holdings volume and the studied economic indicators was noted. The research can be used in design of the regional development programs, in forming budget priorities of budgets projects, or in taking other management decisions programming the basis for effective social and economic policy of the regions
Quantitative evaluation of defect-models in superconducting phase qubits
We use high-precision spectroscopy and detailed theoretical modelling to
determine the form of the coupling between a superconducting phase qubit and a
two-level defect. Fitting the experimental data with our theoretical model
allows us to determine all relevant system parameters. A strong qubit-defect
coupling is observed, with a nearly vanishing longitudinal component. Using
these estimates, we quantitatively compare several existing theoretical models
for the microscopic origin of two-level defects.Comment: 3 pages, 2 figures. Supplementary material, lclimits_supp.pd
A tunable rf SQUID manipulated as flux and phase qubit
We report on two different manipulation procedures of a tunable rf SQUID.
First, we operate this system as a flux qubit, where the coherent evolution
between the two flux states is induced by a rapid change of the energy
potential, turning it from a double well into a single well. The measured
coherent Larmor-like oscillation of the retrapping probability in one of the
wells has a frequency ranging from 6 to 20 GHz, with a theoretically expected
upper limit of 40 GHz. Furthermore, here we also report a manipulation of the
same device as a phase qubit. In the phase regime, the manipulation of the
energy states is realized by applying a resonant microwave drive. In spite of
the conceptual difference between these two manipulation procedures, the
measured decay times of Larmor oscillation and microwave-driven Rabi
oscillation are rather similar. Due to the higher frequency of the Larmor
oscillations, the microwave-free qubit manipulation allows for much faster
coherent operations.Comment: Proceedings of Nobel Symposium "Qubits for future quantum computers",
Goeteborg, Sweden, May 25-28, 2009; to appear in Physica Script
Rare earth spin ensemble magnetically coupled to a superconducting resonator
Interfacing superconducting quantum processors, working in the GHz frequency
range, with optical quantum networks and atomic qubits is a challenging task
for the implementation of distributed quantum information processing as well as
for quantum communication. Using spin ensembles of rare earth ions provide an
excellent opportunity to bridge microwave and optical domains at the quantum
level. In this letter, we demonstrate magnetic coupling of Er spins
doped in YSiO crystal to a high-Q coplanar superconducting
resonator.Comment: 5 pages, 3 figure
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